RF inductively coupled plasma (ICP) sources are widely applied in plasma processing technologies for manufacturing of semiconductor chips (etching, deposition, ion implantation, sputtering, pure silicon production), in the large panel display industry, micro-machine production, nanotechnology, and as the basis for ion sources [see Industrial Plasma Engineering”, v. 1, by J. Reece Roth, “, pp. 391-413 (IOP Publishing Ltd, 1995)]. These types of sources are popular because of their ability to maintain high density plasmas at a relatively low operating gas pressure.
For a typical ICP source with an inductor coil wound on the surface of a vacuum-sealed port of an insulator, and driven at 13.56 MHz, at the active RF power consumed in plasma of about 1 kW, the inner volume of the discharge chamber is a few liters, and the operating gas pressure is in the range 1-100 mTorr, the resonant RF current of the coil is a few tenth of amperes, and the RF voltage across the coil is a few kV [see for example FIG. 11.16 in the publication “Industrial Plasma Engineering”, v. 1, by J. Reece Roth, p. 413 (IOP Publishing Ltd. 1995)]. The RF power loss at these conditions in the matcher, connectors, and at the inductor coil is about the same as consumed in plasma. Besides that, proximity of the coil and metallic walls of the discharge chamber leads to an additional power loss in these walls due to inductive heating caused by eddy currents. The high value of the RF voltage (few kV) applied across the inductor coil causes flow of a considerable capacitive current through the coil, dielectric, and plasma to the chamber walls. This physical process builds a high negative dc potential on the surface of the insulator facing the plasma thereby accelerating the plasma ions toward this surface and causing surface erosion, plasma contamination, and an increase of plasma dc potential reference with respect to the chamber, all at the same time.
To overcome the considered problems, the ferrite core 1 with an actual primary winding 2 can be set within the discharge chamber 3 as is shown in FIG. 1, illustrating the Prior Art [see E. Shun'ko, U.S. Pat. No. 5,998,933], to induce around the core an alternating vertex electrical field E capable of accelerating the electrons and exciting and maintaining plasma within the discharge chamber 3. However setting the bare ferrite core with the primary winding directly in the discharge chamber is not desirable for technologies requiring a high purity in the process. Taking into account that the drop in potential experimentally measured on the closed loop around the core is about 100 V, assumes that the coil of the primary winding, comprising a minimum possible 1 turn, should also have about a 100 V drop, one can conclude that a considerable density of the ions accelerated to the energy level of about 100 eV can be expected in the plasma and will bombard the coil and the core causing plasma contamination and possible damage to the substrate. Setting the bare ferrite core with the coil in the discharge chamber also creates a problem with the core and coil cooling necessary for long lasting proper operation of the inductor at a certain power value. To avoid this problem, one can envelope the core and the coil in a dielectric or in a cooled metallic jacket having an electrical gap around the core, to prevent an electrical shortage, and vacuum sealed to provide the coolant (air) circulation [see U.S. Pat. No. 5,998,933 by E. Shun'ko; US Pub. No. 2003/0015965 A1V by V. Godyak]. However the design and the practical realization of these jackets meet a plurality of the obvious and latent engineering problems due to relative complicacy of these embodiments
There is the possibility of avoiding the considered problems by building an external bridge connecting one part of the discharge chamber with another one by a bent metallic tube with a short insulating pipe inserted (to avoid shortage in the discharge counter) and passing throughout the circular ferrite core(s) having the primary winding(s) [see U.S. Pat. No. 6,392,351 B1 by E. Shun'ko,]. However about half of the plasma volume generated by this type of plasma inductor is wrapped within the tube of the same external bridge, and the energy of this part of the plasma is dispersed in the tube walls providing useless and undesirable heating.
The present invention enables one to overcome all the problems considered above by insertion of a discharge chamber equipped with corresponding small bone-shaped ports of an insulator in gap(s) of the quasi-closed high permeability (ferrite) core disposed in a coil of a primary winding.